What you NEED and what you want may be different things, depending on budget.
For reference, I'm playing Arma3 with the following mid-range kit and get the same frame rates as everyone else on our public server at the moment. Settings on High/VHigh except AA down to 2x. If you're happy with 30fps, which I am, you don't need to break the bank to achieve it, and more powerful components don't necessarily mean better performance if the server is limiting the frames delivered.
Yes, if I had the cash I might upgrade, but it would be more WANT than need.
i5-2500K, 3.3GHz
ATI HD5850 1Gb
8Gb
SSD 128Gb
Win7 64bit, 1920x1080
